Multiply Excess

Recur (If you cast this spell from your hand, exile it as it resolves. At the beginning of your opponent's next upkeep, you may cast this card from exile without paying its mana cost.)
Until end of turn, whenever a creature enters the battlefield under an opponent's control, that player puts the top X cards of his or her library into his or her graveyard, where X is that creature's converted mana cost.